1. Field of the Invention
This invention relates to an optical disc for recording/reproducing data, in terms of an encoding block as a unit, and an optical disc device employing this optical disc.
2. Description of the Related Art
In an optical recording medium, such as a read-only optical disc, a write-once optical disc or an overwrite optical disc, there is occasionally produced an error in reproduced data due to disc defects or contaminants deposited on its recording surface.
Such disc defect or the data error caused by dust and dirt render unstable the servo operation of controlling the disc rotation. This data error is liable in turn to cause further data errors. In order to combat this inconvenience, it is customary with the optical disc to append parity bits for error correction to recording data.
In a data structure disclosed in Japanese Laying-Open Patent H-8-346108, a two-dimensional array of 172 words by 192 rows represents an ECC block, as shown in FIG. 1. That is, in the C1 direction in the drawing, referred to hereinafter as the PI direction, 10-word parity bits to 170 words are appended to the data, so that 172 words of data and 10 words of PI parity make up a column. 192 such columns are arrayed and 16-word parity bits (PO parity) are appended in the C2 direction, referred to hereinafter as the P0 direction.
These PI and PO parities are parity bits for error correction by the Reed Solomon product Code (RPSC).
This ECC block is split in recording units termed sectors. A number of the ECC blocks are recorded on the sector basis on a track of the optical disc. This sector is obtained by dividing the ECC block of 32 KB data into 16 equal portions such that each divided portion represents a data unit of 2 KB.
In this ECC block, each sector is made up of 13 columns, each ECC block being made up of 16 sectors, as shown in FIG. 2. This sector is made up of 12 columns of the data area of the ECC block and a column of the PO parity.
Recently, a demand is raised for an optical disc of a higher density and a larger capacity than the digital video disc in order to enable recording of a larger volume ofdata.
It is assumed that, in a high-density optical disc having the recording density of the optical disc of the digital video disc standard doubled in the track direction, the disc defect and the dust size are the same as those of the above-mentioned digital video disc. In this case, the correction capability of, for example, not less than 5 mm in terms of the length of the track is required for error correction. Thus, the correction capability of a data volume larger by an amount corresponding to improved recording density than with the conventional optical disc is required.
If, in an optical disc having increased recording density for coping with high recording density, an equivalent code to that of a digital video disc is used with an equivalent redundancy, an equivalent error correction is achieved. However, it is not possible to provide a correction capability of not less than 5 mm in terms of the track length.
In view of considerable difficulties in increasing the recording density, it is not desirable to increase the redundancy due to the logical format. Moreover, it is desirable to improve the correction capability for correcting the errors due to dust or scratches on the substrate especially if a thin substrate of the optical disc is used.